Guy Kawasaki explains how to use LinkedIn's Reference Check Tool to avoid bad bosses.  In essence, you can input a company name and a range of years to find people who worked at the company during a given time period. 

This would be a great tool for locating potential witnesses in a litigation action.  Input the plaintiff/defendant company name and the years before, during and after the actionable conduct.  LinkedIn will serve up a list of people who may know a bit about company/facts/etc.  Even better, they may no longer be employed and more likely to help you.